Method of making controlled buoyancy electrical strand

ABSTRACT

A fine expendable wire strand with a slow, predetermined sinking rate in sea water is formed of enamel-film insulated conductors covered, along with a tensile strand, by a polymeric foam, interspersed with glass bubbles.

United States Patent 1 1 1 3,902,937

Arndt et al. 1 Sept. 2, 1975 [54] METHOD OF MAKING CONTROLLED 2,518,454 8/1951) Elliott 174/110 F BUOYANCY ELECTRICAL STRAND 2907.075 10/1959 Ncwby 174/1 1() F 3,030,215 4 1962 Veatch ct a1. 174/116 1 lnvenwrsl Rudolph William 3,064,073 11/1962 Downing ct 211.. 174 110 F Ulmer; Daniel G. Stone, all of 3,278,673 10/1966 Gore 1 156/51 Muskegon, Mich. 3,336,184 8/1967 Stustny ct a1. 156 79 3,343,984 9/1967 Saums ct a1... 117/231 1 1 Asslgneei The Anaconda p w New 3 517,110 6/1970 Morgan 174/101.5 York. 3,565,685 2/1971 Suzuki 117/218 3.573976 4/1971 Duane 117 232 [22] 1973 3,687,748 8 1972 Clock ct 111. 174/110 F 2 App] 330 33 3,699,237 10/1972 Mclia 174/110 F 3.744.016 7 1973 Davis 174 101.5

Related U.S. Application Data Division of Ser. No. 215,858, Jun. 6, 1972, Pat. No. 3.740,454.

U.S. CL"... 156/51; 156/79; 156/315; 427/119 lnt. Cl. H018 7/02; HOlB 13/16 Field of Search 174/70 R, 101.5, 110 F, 174/113 R, 111, 115. 120 C, 116i 156/48,

51, 79, 244, 315; 117/232, 231; l6l/DIG. 5

References Cited UNITED STATES PATENTS 2/1935 Fletcher 174/115 Primary ExaminerDouglas J. Drummond Assistant Examiner-Basil .l. Lewris Attorney, Agent, or Firm-Pennie & Edmonds [57] ABSTRACT A fine expendable wire strand with a slow, predetermined sinking rate in sea water is formed of enamelfilm insulated conductors covered, along with a tensile strand, by a polymeric foam, intetspersed with glass bubbles.

3 Claims, 2 Drawing Figures METHOD OF MAKING CONTROLLED BUOYANCY ELECTRICAL STRAND This is a division of application Ser. No. 215,858. filed Jan. 6. 1972. now US. Pat. No. 3.740.454.

BACKGROUND OF THE INVENTION tors and sea water. It would be desirable that the strand not sink too rapidly upon being deposited in the sea. but. on the other hand. it should sink to the bottom within a reasonable time and not remain floating after it has been discarded. It should be possible to manufacture the strand on available wire insulating equipment. in large quantities. at reasonable cost.

SUMMARY We have invented a controlled buoyancy strand which satisfies the hitherto unobtainable combination of desiderata comprising at least one. and preferably. in parallel, two, or more. elongated electrical conductors. such as copper wires. insulated with enamel film, such as polyurethane film. Our strand preferably also comprises at least one tensile member. parallel to the conductors. Buoyancy is supplied to our strand by an element. such. preferably as an elongated encasement, comprising a polymeric foam and at least 4 weight percent and. preferably, no greater than 20 weight percent of glass bubbles dispersed in the foam. Preferably our encasement will have a circular section. will have a diameter no greater than 0.04 inches. and will have a composite density only slightly exceeding the density of sea water. We have found plasticizcd polyvinyl chloride is particularly suitable for the foam of our strand and that the glass bubbles may advantageously have an average particle density that does not exceed about 0.35 grams per cubic centimeter.

In our new method of making a controlled buoyancy strand we film-coat at least one electrical conductor wire with magnet wire enamel. We blend a mixture comprising 75-96 parts by weight of a polymeric organosol, 425 parts by weight of glass bubbles. and 0.1-2.0 parts by weight of blowing agent. We continuously pass the conductor, coated with the enamel. along with at least one tensile member. through an enameling applicator and therein cover the member and the wire with a layer of the mixture. Then we pass the strand through a heating zone. therein activating the blowing agent and forming the organosol. Preferably several applications of the mixture will be applied, followed each time by passage through the heating zone. We may also apply coatings of the polyvinyl organosol free from blowing agent but comprising the dispersion of glass bubbles, preferably before and after the application of organosol and glass bubbles comprising blowing agent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a section of a strand of our invention. FIG. 2 shows a plan of the steps of the method of our invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT A two conductor embodiment of our strand is indicated generally by the numeral 10 of FIG. 1. Two fine copper wires I1. 12 are insulated respectively with films l3, 14 of polyurethane enamel. We have preferred the use of polyurethane because it bonds particularly well to a polyvinyl encasement 16, but other enamels. known as magnet wire enamels such as polyvinyl formal, polyester. polyimide-amide, polyimide, epoxy. nylon, polyacrylie and polyolefin are well suited for use in our invention. The thickness of the enamel films 13, 14 will be no greater than that required for a desired degree of insulation resistance. since the film. being non-porous and solid in section. will have a higher density than the encasement I6. Typical thickness of the films 13, 14 in the illustrated embodiment will approximate 0.1 mil on Awg 39 (0.0035 inch) wire.

The wires ll, 12 are laid parallel in the strand I0. This has the advantages that no wire twisting step is required with attendant expense and possible damage. particularly to such fine wire, that the capacitance can be lowered by separating the two wires, and that no problem is presented of uniform distribution of the encasement 16 into interstices of a twisted strand. Voids at the interstices of twisted wires would result in unde' sirable variations of density. Where these advantages are relatively unimportant. however. which may be the case with larger conductors. twisted wires may be used within the scope of our invention. A tensile member 17 is laid parallel to the wires ll, 12 to prevent them from elongating due to the stresses of dereeling. and of any water drag that may occur. We prefer to use a cottonpolyester thread having a breaking strength in excess of 2 pounds for the member 17. Other fibers such as pure cotton or polyester, rayon. linen. and silk may be used as may also glass or metals such as stainless steel. but these latter have the disadvantage that increased encasement volume is required to compensate for their weight and the steel would detract from electrical properties.

The novel structure of the encasement I6 constitutes an essential feature of our invention. This comprises a polymeric foam portion 18 within which are dispersed a large plurality of very small glass bubbles l9. Organosols suitable for the portion 18 are commercially available. An organosol is described in the Condensed Chemical Dictionary published by Reinhold Publishing Corporation as a colloidal dispersion of any insoluble material in an organic liquid. but more specifically. the finely divided dispersion of a synthetic resin in plasticizer. with or without solvents or other materials." Organosol" in this application refers to the more specific definition. The organosol of foam I8 is polyvinyl chloride and it is made to foam by the inclusion of a blowing agent. of which a number of types are commercially available. We have preferred to use N,N dinitroso-N,N- dimethyl terephthalamide because of the fine structure of the foam created and its low release temperature (105C It is important that the blowing agent selected should produce a closed cell structure. The polymeric foam would. in itself. be capable of imparting M [h d f M t e o o anu ac ure buoyancy to the strand 10 but we have discovered that the dispersion of glass bubbles within the foam struc- The preferred method of manufacturing the strand of ture not only enables us to control the strand density our invention is well illustrated by the method used for within fine limits. but unexpectedly results in a much 5 the strand of EXAMPLE Ill. above. A composition A smoother strand surface. Smoothness is important to was prepared by screening B 22A glass bubbles. supstrand handling both in production operations and deplied by 3M Company and discarding all bubbles that position at sea. were retained on a standard 170 mesh screen. A mix- By glass bubbles we refer herein to very small hollow ture was then prepared of a polyvinyl chloride organoglass spheres such as those sold as Micro balloons lC l sol having a viscosity of 1900-1950 cps at 20C. a 101 by Emerson & Cuming lnc.. Canton. Mass. and Shore Durometer hardness (after cure) of D 49, a sold as glass bubbles by the 3M Company of St. Paul. cured tensile strength at 25C of 2250 psi and an elon- Minn. Glass bubbles are available in nominal average gation of 227%; and 8% of the weight of the organosol densities from 0.20 to 0.37 grams per cubic centimeter. of the separated fine glass bubbles. Composition B was The higher densities are due to greater glass wall thickl prepared. as above. but with 7.9% of glass bubbles and nesses that may be required to withstand high pres- 0.7% of blowing agent (Nitrosan. supplied and tradesures. We have employed glass bubbles of 0.20 grams mark registered by E. l. du Pont de Nemours and Co.. per cubic centimeter average density and prefer to he. Wilmington. Del.). Composition C was prepared.

keep the density to 0.35 grams per cubic centimeter for identical to composition A but with 5.5% of the bubreasons of economy and lower strand diameter. We 30 bles. Two Awg No. 39 copper wires 31. 32 insulated have found that glass bubbles passing through a l70 with polyurethane film by paying them from spools 33,

inch screen should be used in the encasement l6 and 34 through a known type of enamelling machine 36. that about 8% by weight of the bubbles based on the (commercial standard Single Analae Wire supplied and weight of foam is optimum. Fewer than 4% will not suftrademark registered by Anaconda Wire and Cable fice to afford the advantages of glass bubble addition 25 Co). and a thread of Polyspun 100 37 supplied by the and higher percentages. such as. in particular. percent- Standard Coosa-Thatcher Co. of Chattanooga. Tenn.. ages over 20 are not properly supported in a foam mafrom a spool 38, were pulled in parallel through an trix. 0.028 inch steel ball enamelling die, 38 and coated with The strand has no outer jacket and the encasccomposition A to a diameter of 0.020 inch. after curment 16 is in direct contact with sea water after the ing. The strand was then passed through an 0.034 inch strand has been deposited possibly except for a very ball die 39 and coated with composition B to a cured thin surface wiped coating of silicone oil lubricant such diameter of 0.028 inch after curing. finally the strand as Dow Corning 510* Silicone. By this means the diamwas passed through an 0.036 ball die 41 and coated eter (I is minimised and the eventual collapse of the with composition C to a diameter of 0.032 inch and.

after curing. wiped with silicone oil by means of felt apfoam. once the strand has sunk to sufficient depths. re-

plicator 42 (DC-510 supplied and trademark registered moves any change of resurfacing.

*Trademark registered by Dow Corning Corp. y Dow Corning Corp. of Nlidldndq Mich Coating EXAMPLE I ll III IV ()rganosol PVC PVC PVC PVC 4 glass 13 abt. 7 5.5-8 l0 glass density. g/cc 0.33 0.28 0.20 0.20 tensile member none cottoncottonglass nylon polyester conductor sire Aug 39 39 3) 3) No. of conductors 2 2 2 2 conductor insulation epoxy polypolypolynylon* urcure urethane thanc thane No. of coats of organosol 5 -l 3 3 strand 01).. inch .036 .03o .032 .035 breaking load. lbs. .45 2.6 2.7 0.8 copper elongation. 1 27 6.5- l l (v I) 5.6 sinking rate. in salt watcr** initially. ft/min 0,4 0.4 l,0 0.9 24 hrs. ft/min 3.4 3.0 0.5 0.9 lR wire to wire ft, samples. thousand megohm in air 200 35 200+ 200+ salt \\'ater** initial 200 200 5 hrs it] 2.5 l0 l5-20 72 hrs 10 0.3 10 15-20 capacitance/ft at l KH/ pf. wire to wire in air 49.2 41.0 2N5 17.7 57.3 54.x 36.5 26.3

Diss. factor. wire to wire at l KHY. I it. 1 in air l2.(i I63 I01 9.2 in salt water 12.7 15.3 (.7 75

*described in patent 3.403.807 Na (l in water. sp. gr. L027 at 25C speed was 30 feet per minute and after each coat the strand passed through a 5-foot horizontal muffle oven 43 maintained at 210C for the first 2 feet and 230C for the last 3 feet of oven space. A cured specimen taken after the first coat exhibited a descent rate of 7.5 feet per minute in the 1.027 gravity salt water. A specimen after the second coat exhibited a descent rate of 2.4 feet per minute.

The foregoing description has been exemplary rather than definitive of our invention for which we desire an award of Letters Patent as defined in the following claims.

We claim:

1. The method of making a controlled buoyancy strand comprising the steps of:

A. film coating at least one electrical conductor wire with magnet wire enamel,

B. blending a liquid mixture comprising:

a. 7596 parts by weight of polymeric organosol, b. 4-25 parts by weight of glass bubbles. e. O. l2.() parts by weight of blowing agent,

C. continuously passing said conductor wire coated with said enamel. along with at least one tensile member, through an applicator suitable for applying liquid magnet wire enamel and therein covering 6 said member, together with said wire, with a layer of said mixture,

D. continuously passing said wire and said member while covered with said mixture, through a heating zone and therein activating said blowing agent and foaming said organosol.

2. The method of claim 1 comprising the additional steps of blending a liquid mixture comprising 96 parts by weight of said polymeric organosol and 425 parts by weight of said polymeric organosol and 425 parts by weight of glass bubbles and free of blowing agent and, after foaming said organosol comprising blowing agent, continuously passing said strand through an applicator suitable for applying liquid magnet wire enamel and therein coating said strand with said mixture free of blowing agent.

3. The method of claim 2 comprising the additional steps of continuously passing said conductor wire coated with said enamel, along with said tensile member, through an applicator suitable for applying liquid wire enamel and therein covering said member, together with said wire with said mixture free of blowing agent, and heating said mixture free of blowing agent, prior to covering said strand with said mixture comprising blowing agent. 

1. THE METHOD OF MAKING A CONTROLLED BUOYANCY STAND COMPRISING THE STEPS OF: A. FILM COATING AT LEAST ONE ELECTRICAL CONDUCTOR WIRE WITH MAGNET WIRE ENAMEL, B. BLENDING A LIQUID MIXTURE COMPRISING A. 75-96 PARTS BY WEIGHT OF POLYMERIC ORGANOSOL, B. 4-25 PARTS BY WEIGHT OF GLASS BUBBLES, C. 0-1-2.0 PARTS BY WEIGHT OF BLOWING AGENT, C. CONTINUOUSLY PASSING SAID CONDUCTOR WIRE COATED WITH SAID ENAMEL, ALONG WITH AT LEAST ONE TENSILE MEMBER, THROUGH AN APPLICATOR SUITABLE FOR APPLYING LIQUID MAGNET WIRE ENAMEL AND THEREIN COVERING SAID MEMBER, TOGETHER WITH SAID WIRE, WITH A LAYER OF SAID MIXTURE, D. CONTINUOUSLY PASSING SAID WIRE AND SAID MEMBER WHILE COVERED WITH SAID MIXTURE, THROUGH A HEATING ZONE AND THEREIN ACTIVATING SAID BLOWING AGENT AND FORMING SAID ORGANOSOL.
 2. The method of claim 1 comprising the additional steps of blending a liquid mixture comprising 75-96 parts by weight of said polymeric organosol and 4-25 parts by weight of said polymeric organosol and 4-25 parts by weight of glass bubbles and free of blowing agent and, after foaming said organosol comprising blowing agent, continuously passing said strand through an applicator suitable for applying liquid magnet wire enamel and therein coating said strand with said mixture free of blowing agent.
 3. The method of claim 2 comprising the additional steps of continuously passing said conductor wire coated with said enamel, along with said tensile member, through an applicator suitable for applying liquid wire enamel and therein covering said member, together with said wire with said mixture free of blowing agent, and heating said mixture free of blowing agent, prior to covering said strand with said mixture comprising blowing agent. 